PSL54C Safety Sear

So I've been hearing about how Century had a recall on PSL's a while back due to the "safety sear" hole being misconstrued as a hole for a full auto sear. Well I've been wondering, would it be possible to install a safety sear inside without having a hole through the reciever? Such a component would allow extra safety for the user without compromising legality.

Anyone have a good diagram of an AK action? I'd like to fiddle with the idea.

The recall was due to improperly welded sear holes, which is not allowed. Example of the bad weld:
http://www.gunjunkie.net/images/guns/recall.gif

The Romanians kept the hammer retarder as an added safety, even on their semi autos, as it wont allow the hammer to drop until the bolt is foreward and locked into battery, which is why even though a semi these receivers had the third hole. The ATF calls this an "auto sear", not a "hammer retarder". It doesn't matter that neither the bolt or trigger parts can be used for any "FA" purposes.